1. Field of the Invention
This invention relates to lens technology, and more particularly, to a lens-aperture control mechanism for use in a lens unit, such as a camera lens, to control the aperture of the lens unit.
2. Description of Related Art
An aperture is a variable opening in a camera lens that controls the amount of light passing through the camera lens to the film. A lens-aperture control mechanism is typically mounted inside the lens barrel, but it can also be mounted at the front or rear end of the lens. FIG. 1 is a schematic perspective view of a camera lens 100 which is incorporated with a single-piece aperture device. As shown, the barrel of the camera lens 100 is formed with an insertion slot 102 which allows a flat single-piece aperture device 200 formed with a number of variably-dimensioned openings 202 to be inserted therein. The single-piece aperture device 200 can be adjusted in position so as to allow one of the openings 202 to be used as the aperture for the camera lens 100. One drawback to this single-piece aperture device 200, however, is that the aperture can be only selected from the two fixed openings 202, and cannot be fine tuned.
FIG. 2 is a schematic diagram showing a conventional two-blade aperture device. As shown, this aperture device includes a pair of blades 210 which can be controllably moved toward or away from each other to allow a controlled amount of light to pass through the space between these two blades 210. This aperture device allows the aperture to be fine tuned to any desired value. One drawback to this aperture device, however, is that the square shape of the aperture would cause the image formed by the light passing this aperture to be unevenly illuminated, particularly at the edge portions of the image.
A conventional lens-aperture control mechanism that can provide a near-circular aperture is the so-called iris diaphragm, which is depicted in reference to FIGS. 3A, 3B, and 3C. As shown in FIG. 3A, the iris diaphragm includes a rotatable ring 212 and a plurality of blades 214. The rotatable ring 212 is formed with a plurality of radial slots 213 spaced at equal angular intervals around the rotatable ring 212. Each of the blades 214 has a first end formed with a pivot 217 and a second end formed with a peg 218 slidably fitted to one of the radial slots 213 in the rotatable ring 212. When the rotatable ring 212 is being rotated, each blade 214 will be pivotally moved, causing the peg 218 to be shifted along a route indicated by the reference letter T. As shown in FIG. 3B, the pivot 217 is fixedly formed on a nonrotatable ring 216, and the plurality of blades 214 are arranged in a circular manner to define an aperture 220 whose diameter can be variably adjusted simply by rotating the rotatable ring 212 with respect to the nonrotatable ring 216. As shown in FIG. 3C, the foregoing iris diaphragm is mounted between a front lens group 112 and a rear lens group 114 inside a lens unit 110 so as to control the amount of light passing through the front lens group 112 and the rear lens group 114 to the film (not shown). The rotatable ring 212 can be driven by a motor (not shown) via the transmission through a gear 219 meshed to the rotatable ring 212.
The foregoing iris diaphragm has the benefit of flexible control over the lens aperture. One drawback to it, however, is that it is quite complex in mechanical construction, which would lead to a high manufacture cost. Moreover, since the iris diaphragm is mounted between a front lens group 112 and a rear lens group 114, it would be difficult for the two lens groups 112, 114 to be precisely aligned along an optical axis.